In May the basement laboratory of Marenna General smelled of hot dust and floor polish and, for three weeks running, of the lilies that somebody on the ward upstairs kept sending to the staff room in the hope of being forgiven.

Sienna took the night shift in the second week. It had been her own idea. Nell's mother was ill, and Nell had a face like a sheet, and there was no one else on the rota who could be trusted with the mass spectrometer after midnight. She had said so to Dr. Pryce, in his cluttered office, across a desk piled with journals, and he had looked at her over the top of his spectacles with an expression of the deepest suspicion. Mrs. Bellandi, he said, was surely not obliged to work nights.

"Mrs. Bellandi would like to," Sienna said.

"Is your husband aware of it?"

"He will be, by six."

Pryce had actually smiled. It was a brief, dry, startled thing, like a crack in a wall, and he had gone on looking at his journals for some time without turning a page. "Very well, Hale," he said, at last. It was the first time he had used her own name since October.

Matteo took it better than she had hoped. He had stood in the library in his shirtsleeves, with a ledger in his hand and a faint line between his brows, and had asked her one question. Would she be at the General, in the same room, with the door shut? She said yes. He asked whether he might bring her supper. She said he might. He asked whether he might sit on the bench by the stairs, as he had once before, and she said that he would do nothing of the kind, he would be at home asleep like a sensible man, and he looked at her with a small crooked smile and said "Of course," in a voice that did not for one moment deceive her.

He was on the bench at eleven.

He had come in the plain gray car, with no Marco, in a dark overcoat with the collar turned up, and the night guard, a stooped gray gentleman named Mr. Aldous who had been at the hospital for thirty-one years and had never been known to remark on anything, had nodded to him at the door and gone back to his crossword. He sat on the wooden bench under the faded poster at the end of the long cold corridor with a tin pail between his knees, the plain tin pail that Mrs. Venn had once used to send her husband's dinner to the quay, and he looked, in the flickering tube light, like a man waiting outside a confessional.

"I said you shouldn't," said Sienna.

"You did." He rose. "I am a very bad listener. It is the chief reason that I am still alive."

They ate at midnight, on the bench, side by side, with the pipes ticking overhead. It was Mrs. Venn's chicken pie, still warm in a cloth, and a flask of strong tea, and a slice of seed cake wrapped in greaseproof paper. Sienna tested the pie. She tested the tea. He watched her do it, with his chin on his hand, and said nothing, and when she had finished he took the paper strip from her fingers and laid it carefully in the pail, as one lays away something precious.

"You keep them," she said.

"Eleven of them. In a drawer." He did not look at her. "I thought you might wish to know."

She put her head down on his shoulder. It was a long moment before either of them spoke, and when he did, it was in a low voice, to the dark of the corridor.

"I should like to say a thing about March."

"You needn't."

"I said I would end it by then. I did not. I signed a lease instead." He drew a breath. "I want you to know that I am still looking. Marco has a man in Carrow, a very patient one, and a second at the Plover Quay warehouse. I have not forgotten. I will not be the sort of man who says March, and then lets April go by."

"It's May."

"I am aware." A thread of rueful humor ran under his voice. "I am keeping a calendar. It is a very depressing object."

She laughed, softly. She turned her face against his coat and felt him bend his head until his cheek rested on her hair. They sat so for several minutes. In the room behind them the mass spectrometer ticked, patient and indifferent, and Mr. Aldous turned a page of his crossword somewhere above them in the hall.

She went in at half past twelve.

She had a reason, and it was a good one. For three weeks she had been turning a thing over in her mind, ever since the library, ever since a little black book had lain open on the green leather with a leaf cut out of it. She had begun to think about the glass. She had thought about it as she thought about every hard result, patiently, in a quiet part of her mind that went on working while the rest of her ate toast and held hands. A harmless compound, sleeping in the etched band of leaves. A cold dry acid, poured into a flute. She knew what woke it. She did not yet know what else could.

If it was an acid, it need not be champagne. That was the question. She wanted to run it again, with the new reagents that had come in April, and she wanted to run it against the old samples, her own, the two tubes she had sealed in October and put away with her initials across the wax.

The cold cabinet was at the back of the little room under the stairs, behind a row of boxes marked EXPIRED. She moved them one by one. They were where she had left them, brown cardboard cartons with their labels curling in the damp. The lockbox was behind the last. It was a small gray steel thing the size of a loaf of bread, with a hinged lid and a strip of white tape across the seam. Her initials stood on the tape in black ink, S.H., in a small upright hand.

She took it to the bench and set it under the lamp.

She did not know what made her look twice. She had not been looking for anything. She had been thinking about reagents, and pH, and the order in which she would load the vials. But her eye had gone to the little black letters on the white tape, as an eye goes to a crooked picture, and something in her trained and patient mind said, calmly: wait.

She took the magnifier from her pocket and bent over the tape.

The S and the H were joined. That was how she wrote them, always, in a single pull, with the pen never leaving the page. A quick, impatient, upright little scrawl. She had written them a thousand times on a thousand labels, and she knew the shape of it as she knew the lines in her palm.

Halfway down the first stroke, the ink thinned.

It was a hair's breadth. A tiny hitch, where a real hand would have kept its speed. And at the end of the second letter, where her own pen always finished with a short hard flick to the right, as her mother's had, as her father's did, there was nothing at all. The H ended clean.

The whole room seemed to go still.

She stood motionless under the lamp. Somewhere a long way off a tap was running. The mass spectrometer ticked. She had the extraordinary sensation of standing on the floor of a room she had known all her life and watching the walls move very slowly outward.

She had seen that hitch in a sterilizer log. She had seen it on a cheque with a dead man's name. And now she was looking at it on her own initials, in her own hand, on a tape that she had sealed with her own thumb. Someone had stood in this room, at this bench, in the dead hours of a night she had not been here, and had written her name.

She broke the seal with a scalpel. She did it steadily. She lifted the lid.

The two tubes were there, side by side in their foam, with their screw caps and their white labels. She knew them. She lifted the first and held it to the light. It was the right size and the right make. The label read, in the small hard hand, Flute 1, rim, 14 Oct. It was exactly as she had left it.

It was exactly as she had left it, with one difference. She had swabbed the rim of the glass with a cotton tip, and snapped the stem into the tube, and the cotton had been pale gray with a faint smear of residue. This one was white. It was clean. It lay in the bottom of the tube like a little white worm, and when she unscrewed the cap and drew it out with the tweezers and held it under the lamp, it was dry, and fresh, and had never touched anything but air.

She stood there with it in her fingers, and her hands began, very slightly, to shake.

She ran it anyway. She ran both. She loaded them into the rack with a meticulous, dreadful, careful patience, and watched the numbers come up on the screen line by line, and they were nothing. Flat. Clean. A trace of the cotton. The faint ghost of a laboratory. Whatever the swabs had held in October was gone. The one piece of evidence she had that the glass itself was the weapon, the harmless sleeping compound that had given her a year of hard sleep and a mathematical certainty, had been taken out of a locked cabinet, behind a row of expired reagents, and replaced with a lie.

She turned off the instrument.

She sat on the stool with her hands flat on her knees and her eyes on the blank screen, and for a long moment she could not feel anything at all. It was only the cold. It rose from the floor, and the walls, and the little steel box on the bench, and settled over her like a hand.

She thought of the lab. It was hers. It was the single place in the whole bright, complicated, frightening world where nobody had ever asked her for anything, where a result was a result and a column of numbers did not lie. She had come into it at twenty with her father's ruined shop behind her and her mother's death before that, and it had been the first room in her life where she felt that she was not being kept. Everything in it was labeled, logged, locked in the proper place. She could have found any vial in the dark.

And someone had come in, and put out a hand, and moved it.

She was angry. She noticed it with a sort of detached surprise, as she might have noticed a change in a trace. It began somewhere under the breastbone, small and hot and bright, and spread outward until it filled her to the fingertips. It was not the anger she had felt in the library, the grieving furious anger of a woman who has been decided for. It was a cold, clean, scientific rage, the kind that comes of finding a contaminated sample in a clean room.

She went to the door and opened it.

He was on the bench where she had left him, and he was on his feet before the latch had finished clicking. He read her face in the flickering tube light, as he always did, as he had read it on a pier at sunset. The color drained out of his own. He took two quick strides toward her, and stopped, dead, a pace from the threshold, with his hands open at his sides.

"What has happened?"

"Someone has been in my lab."

"When?"

"I don't know." Her voice was very level. "Some night in the last seven months. They had a key to the cold cabinet and my handwriting." She drew breath. "They took the swabs, Matteo. The flutes. The only thing I had. They put clean ones in their place and signed my name on the seal."

He did not speak. She saw the stillness come over him, from the shoulders down, the old quiet going-out of the whole man. His eyes went past her into the little room, to the gray steel box under the lamp, and she saw them take in the broken tape and the open lid. He took a step, and she put up her hand.

"Don't."

He stopped at once.

"Not yet," said Sienna. "I'm sorry. It isn't you. I only need it to be mine for a minute."

"It is yours." His voice was low and gentle. "It is yours. I shall stand exactly here."

She looked at him standing on the cold concrete in his dark coat, with his hands open and his eyes dark with a fear that he was plainly doing his utmost to keep from her. And she thought: he could have gone in. Any man would. He could have walked across the room and picked up the box and begun to give orders, and I should have let him, because I was frightened. He is standing in the passage like a man at the edge of a chalk line.

Her eyes stung.

"What do you want?" said Matteo.

It was asked very quietly. It was not an offer, and it was not a plea. It was a plain question, put to her as to an adult, in the middle of the night, by a man who had once, in a dark passage, decided for her what she could bear. She heard it go through her, and she understood, with a quick fierce rush of something that was very nearly love, that he was giving her the rule back.

"I want to stay," she said. "I want to finish my shift. I want to start again from the beginning, with fresh swabs, from the glass itself, and not stop until it's done."

"Then we shall."

"The flutes are in the library cabinet."

"I know where they are." He had already taken the telephone from his pocket. "Marco will have them here in forty minutes. Sealed, in the blue box, with a man to carry it who will not let it out of his hand. I will tell him to bring it to the side door, and to wait."

"And you?"

"I shall go wherever you wish." A faint, tired smile. "On the bench, or in the car, or at the bottom of the stair."

She looked at him for a long moment.

"Inside," said Sienna.

He stood very still.

"I want you in the room," she said. "Not at the bench. Not in the way. I should like you to hold the lamp. I think," she said, and her voice cracked a little, "that I should rather not be alone in here again tonight."

The breath went out of him slowly. He did not say anything. He crossed the threshold, as he had crossed the sill of the green room on the night of the first of December, as though it were a line drawn on the floor in chalk, and she moved aside to let him pass. She did not ask him to be careful of anything. She did not need to. He walked into the little room under the stairs like a man entering a church.

Marco came at ten past one.

He did not say a word. He handed over the blue leather box at the side door, sealed with red wax, and stood with his hat in his hand and his broad face rigid as granite while Sienna broke it, and inspected the lining, and lifted out the first of the two tall flutes with a pair of cotton gloves. He saw the room. He saw the open lockbox and the white tape and the little pile of cotton. He turned and went out into the corridor and took up a position at the door that could not have been more eloquent if he had been carved over it. She heard Mr. Aldous, up the stairs, drop his pencil.

She worked for three hours.

It was a thing she did well, and she did it carefully, with Matteo at her left shoulder holding the green-shaded lamp. She swabbed the rim of the first flute, and the second, and the etched band of leaves on each, and the base of the stem. She sealed each tube with her thumb and signed it with a pencil, and then, with an odd tenderness, she signed it a second time in the lower corner with an S so small and so quick that a stranger would not have seen it. She loaded the instrument. She waited. And the trace came up, line by line, pale and clear on the blue screen, and there it was, the faint, narrow, patient peak far to the left, where there should have been nothing.

She let out her breath.

"There," she said. "That's it."

"The same?"

"The same." She laid her hand flat on the bench. "It was never in my head."

"No," said Matteo, very quietly. "It was never in your head."

She did the rest by the clock.

She had a fresh bottle of cheap champagne from the staff room, left over from somebody's retirement, and she poured a few drops over the swab and watched the trace shift. A second peak climbed out of the first like a bud opening, sharp and bright and different in shape, and she took a deep breath and read it. It was the thing. It was the awakened thing, the quiet salt of a trap turned into the trap itself. She ran it again. She loaded a small plate of the cultured cells that the department kept for its own use, and added a single drop. In twenty minutes they were dead.

She took a lemon from the staff room.

It was a dry, wrinkled, ancient lemon, left in a bowl since Christmas. She cut it with the scalpel, and pressed a drop of the juice onto a fresh swab from the etched band, and ran it. She watched the screen. A long dim wait. And then, as slowly and deliberately as a sunrise, a peak climbed out of the baseline, in exactly the same place, and stood there.

"Oh," said Sienna.

It was hardly more than a breath. She stood with her hands pressed to her mouth and looked at it. She felt Matteo move beside her, a quick close warmth at her shoulder, and she did not turn her head.

"It does not need the champagne," she said. "That was only the one that was used. It wakes in anything acid enough. Champagne is about three and a quarter. Lemon juice is two." She heard her own voice, very steady and very far away. "Lemonade. Vinegar in a salad dressing. A glass of orange squash. It would take anything that is sour. And it would work faster."

The lamp in his hand had begun to shake.

She did not look at it. She knew what he was seeing. She knew it as one knows a smell from childhood. It was not the glass, or the box, or a hundred-and-forty-year-old tradition. It was the whole of the house. It was a kitchen full of lemons, in a house where a woman had kept a bowl of them on the sill every spring for forty years.

"Sienna," said Matteo.

"Yes."

"If it is that simple."

"It isn't simple." She drew a breath. "It is only quiet. Someone has to have prepared the glass. It has to be the right glass, and the right hand, and the right sour thing poured into it. But once it is done, a person might use it again." Her eyes came up to his. "It might be done again. It might be done tomorrow, and it would look like a bad lemon."

He set down the lamp.

He did it with great care, as though it were made of glass. Then he turned to her, with the lamplight gone and only the cold blue glow of the screen on his face, and put his arms round her. He did it without asking. She felt it, the one omission in months, and she understood it, and she turned into him and put her forehead against his collarbone and held on with both hands.

He did not say anything. He held her. They stood so for a long time in the narrow blue-lit room, with the dead cells in their plate and the broken tape on the bench, and the quiet of the great sleeping hospital going on above them.

She woke him at four.

He had gone to sleep at the bench. She could not have said when it happened. He had sat down, quietly, on the other stool, with his elbows on the steel and his head in his hands, while she was preparing the last of the controls, and she had looked round a quarter of an hour later and found that he had slid forward until his cheek rested on his folded arm. The lamp was still in his fist. His coat had fallen open. The shadows under his eyes were gray in the blue light.

She stood looking down at him for a long time.

She thought of a man in a study who had not slept in two years. She thought of a long cold corridor, and a bench, and a plain tin pail. She thought of eleven paper strips in a drawer, and she felt something give way in her chest, quietly, like a thread that has been under strain for a very long time.

She took off her own white coat, and laid it across his shoulders. It was too small. It barely covered him. She stood with her hand resting on the back of his neck, light and warm, and he did not stir.

I will tell him tomorrow, she thought.

It was the eighth time. She knew it, and the thought was so tired and so gentle that it did not even hurt. She had a small, cold, ordinary list in the back of her mind, on a page she did not look at, and at the top of it was a single question, and it had been there for five months. A boat in brown paper. A line in a dead man's hand. A drawer in a study. She would ask him tomorrow, when the thing with the glass was settled, when the house was safe, when there was no lemon in the kitchen and no bell about to ring.

She was very tired. She sat down on the stool beside him. She put her head on her folded arms, on the cold steel, with her face turned toward his sleeping one, and looked at him in the pale blue light until her own eyes closed.

The telephone woke her.

It was her own. It shrilled against the steel of the bench like an insect, and she was on her feet before she knew that she had moved, with her heart slamming and the white coat slipping from his shoulders to the floor. The clock on the wall said ten past five. Gray light was showing in the high basement window. Matteo had lifted his head, white, with a crease down one cheek, and was looking at her with the enormous startled eyes of a child.

She snatched it up.

"Hale?"

It was Nell. She had never in six years heard her voice sound like that. It was very small, and very high, and trying with all its might to be steady.

"Nell. What is it? What's wrong?"

"I came in early. I had the paperwork, you know, for Mum, and I thought I'd get a head start before the day shift, and I went to hang up my coat." She drew an unsteady breath. "Hale, I'm in the changing room. It's your locker."

The room did not change. The light did not change. The screen of the mass spectrometer glowed on, blue and blank.

"What about my locker?" said Sienna.

"Someone has been in it," said Nell. "The door's open. They've forced the lock. Everything's on the floor. Your coat, your bag, your lunch box, all of it, and your notebook is gone." A little cracked sob. "And Hale, the bench by the door. I think someone's been sitting on it for hours. It's still warm."